<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
	<?php 
		$a = " Welcome to this class!"; 
		$b = explode(" ",$a); //将$a拆分为多个字符串保存到一个数组$b
		$a = implode(",", $b); //将$b中各元素组合为一个字符串$a
		echo $a;  
	?> 
	</body>
</html>